1. Field of the Invention
The invention relates to a liquid crystal display device that is used in display portions of electronics devices and a manufacturing method thereof.
2. Description of the Related Art
A liquid crystal display device is advantageous in comparison with a CRT (Cathode Ray Tube) in that it is thin, light, capable of driving at lower voltages and low in the power consumption. Accordingly, the liquid crystal display device is used in display portions of various kinds of electronics devices such as TV receivers, note-type PCs (personal computers), desktop computers, PDAs (portable terminal assistants) and portable telephones. In particular, an active matrix liquid crystal display device where a TFT (Thin Film Transistor) is disposed as a switching element to each of pixels (sub-pixels) shows excellent display characteristics comparative to the CRT owing to high drivability and has become being widely used in fields where CRTs have been used such as desktop computers and TV receivers.
A liquid crystal display device generally has two substrates provided with a transparent electrode and a liquid crystal layer disposed therebetween. In the liquid crystal display device, a predetermined voltage is applied between the transparent electrodes to drive the liquid crystal and thereby to control the light transmittance of each of pixels to obtain a desired display. In recent years, a demand for liquid crystal display devices is increasing and requirements for liquid crystal display devices are becoming versatile. Among the requirements, an improvement in display quality is particularly strong. In order to obtain excellent display that is free from brightness irregularity, a technology where columnar spacers are formed on a substrate to control a thickness of a liquid crystal layer (cell gap) uniformly is becoming a main stream.
Existing columnar spacers are disposed in a predetermined arrangement pattern in a substrate plane. With the columnar spacers, a gap between a thin film transistor (TFT) substrate and an opposite substrate disposed opposite to the TFT substrate that are mutually adhered is supported. As a columnar space forming material, a resin material such as an acrylic resin or a novolak resin is generally used. However, the resin materials have an elastic deformation region and a plastic deformation region based on their physicality. When a localized force is externally applied on a liquid crystal display panel, the columnar spacers show plastic deformation and do not return to an original height even after the localized force is eliminated. Accordingly, at a weight-applied portion where the localized force is applied, the irregularity of the cell gaps are caused.
In order to inhibit the cell gap irregularity from occurring, the liquid crystal display panel may well be hardened by increasing the number of spacers or making an area of the column of the columnar spacer larger. However, when the density of the columnar spacers is made too high, when a volume of the liquid crystal decreases under low temperatures, the columnar spacers cannot follow to deform. Accordingly, there is a problem in that, inside of the liquid crystal display panel, a vacuum area is generated and therein an air bubble is generated. As a result, the arrangement density of the columnar spacers cannot be increased so high, that is, there is a restriction on the arrangement density. With the columnar spacers having the arrangement density under the restriction, the resistance of the cell gaps against the external localized force cannot be sufficiently obtained.
In order to overcome the foregoing problems, a patent document 1 discloses a technology where two kinds of columnar spacers different in height are formed. Furthermore, a patent document 2 discloses a technology where columnar spacers are arranged in two or more kinds of arrangement patterns, and, by making use of a step of a film thickness on a TFT substrate side, substrates are stacked to form two kinds of columnar spacers substantially different in height. Liquid crystal display devices described in patent documents 1 and 2, being provided with first columnar spacers that maintain the cell gap at room temperature and low temperature and second columnar spacers for maintaining the cell gap when the localized force is applied, has a structure that does not generate air bubbles at low temperatures and can withstand the externally applied localized force as well.
[Patent document 1] JP-A-2001-201750
[Patent document 2] JP-A-2003-156750
However, when a liquid crystal display panel of a liquid crystal display device is surface pressed, a displacement is caused between the TFT substrate and the opposite substrate to result in light leakage.